Vehicle emission control systems may be configured to store refueling vapors, running-loss vapors, and diurnal emissions in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The stored vapors may be routed to engine intake for combustion, further improving fuel economy for the vehicle. In a typical canister purge operation, a canister purge valve (CPV) coupled between the engine intake and the fuel vapor canister is opened, allowing for intake manifold vacuum to be applied to the fuel vapor canister. Fresh air may be drawn through the fuel vapor canister via an open canister vent valve. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
However, there are circumstances where undesired evaporative emissions (e.g. hydrocarbons, or fuel vapors) may be introduced to atmosphere if mitigating action is not undertaken to prevent such an occurrence. In one example, a CPV, due to frequent use and harsh operating environment, may become degraded. In the case of a degraded CPV, during a refueling event fuel vapors may be introduced to engine intake and then to atmosphere via the degraded CPV (e.g. CPV stuck at least partially open or unable to fully close), rather than being routed to the fuel vapor canister for storage. Furthermore, in such a situation, vehicle stall and/or driveability issues may result post-refueling due to a rich amount of fuel vapors in the intake of the engine, and the first engine crank post-refueling may additionally introduce undesired emissions to atmosphere.
In another example, undesired evaporative emissions may be introduced to atmosphere under situations where vehicle operating conditions and/or environmental conditions result in breakthrough of fuel vapors from a canister. For example, engine run time in hybrid electric vehicles (HEVs) and plug-in hybrid vehicles may be limited, and thus opportunities for purging fuel vapor from the canister may also be limited. If the vehicle is refueled, saturating the canister with fuel vapor, and then parked (or stopped, as in a start/stop event) in a hot, sunny location prior to a purge event, the canister may desorb fuel vapors as it warms up, leading to bleed emissions. In another example, if the canister is at least partially filled with fuel vapor, a refueling event may further load the canister and lead to bleed emissions.
The inventors herein have recognized the above-mentioned issues. The inventors have herein additionally recognized that due to the limited engine run time in hybrid vehicles, in addition to the fact that current and future engines are being designed to reduce intake manifold vacuum as vacuum is a pumping loss, a purge pump positioned between the canister and the CPV is being introduced into such vehicles. Thus, the inventors herein have recognized that the purge pump may be utilized to mitigate release of undesired evaporative emissions and/or driveability issues under conditions of a degraded CPV, or under conditions where bleed through emissions from a canister are indicated to be occurring. Thus, the inventors herein have developed systems and methods to address such issues. In one example, a method comprises controlling an amount of pressure directed to a fuel tank that supplies fuel to an engine of a vehicle, and to a fuel vapor storage canister receiving fuel vapors from the fuel tank, via a pump positioned downstream of the fuel tank and the canister, to actively route fuel vapors to the canister during a refueling event where fuel is added to the fuel tank. In this way, refueling vapors may be prevented from migrating to engine intake under conditions where a CPV is degraded, which may reduce opportunity for vehicle stall and which may improve driveability at the next engine start event, and which may further reduce the release of undesired evaporative emissions to atmosphere.
In one example, the pump may include the engine. In such an example, directing pressure to the fuel tank and to the fuel vapor storage canister via the pump may include rotating the engine unfueled in reverse. In another example, the pump may include a purge pump positioned in a purge line coupling the engine to the canister, and wherein directing pressure to the fuel tank and to the fuel vapor storage canister may include rotating the purge pump in a reverse-mode of operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.